Circuit element mounting unit for electrical measuring apparatus



May 14, 1940- F. s. Fox, JR., Er A1. 2,201,106

CIRCUIT ELEMENT MOUNTING UNIT FOR ELECTRICAL MEASURING APPARATUS Filed Nov. 26, 1937 2 Sheets-Sheet l TJ. 1. T1 En. 3*1 541 56 5,6 5456 :1 f 54 60 40 5 ,'l' 5837 82 55- 50 37d@ 86 8--68 84 I j g 70 744 B Q Jltg 40` gl? 4l 4m; lil 85: 74 D@gu 152 E@W @D 76 F@ {li}III|||||||||||||||l|||||||lIl: 86: 7i -A 74 s@ @f4 i 4W@ "W 'T4 4T' W4 @M-' WWIHHIHUHL mi@ 72 i 5g-@ 35 Q 88j`68 lNvENTO S Frank OQLJJ: Bygeoiye Wash,

May 14, 1940- F. s. Fox, JR.. er AL 2,201,106

CIRCUIT ELEMENT MOUNTING UNIT FOR ELECTRICAL MEASURING APPARATUS Filed NOV. 26, 1937 2 Sheets-Sheet 2 43 2" 156 /l' @D W 58 o o o A O :11:2 B

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COUPLE RANGE NORK lNvl-:NTORS Fran/n S. Fox, Jr.

Patented May 14, 1940 CIRCUIT ELEMENT MOUNTING UNIT FOR ELECTRICAL MEASURING APPARATUS Frank S. Fox, Jr., and George C. Walsh, Foxboro, Mass., assignors to The Foxboro Company, Foxboro, Mass., a corporation of Massachusetts Application November 26, 1937, Serial No. 176,769

'7 Claims.

This invention relates to electrical apparatus` of electrical measuring apparatus in which they are incorporated. m The present trend toward more accurate measurement andl control of industrial processes has increased the demand for electrical apparatus for accurately indicating, controlling, and/or recording values `of conditions, and more particularly for potentiometric or similar instruments for measuring temperature and other conditions of such processes This demand has increased also the need for expanding the scale of manufacturing and servicing of this'type of apparatus. .0 While the manufacture and assembly of the structural parts of such instruments has been largely standardized and simplified, the Wiring hook-up has not because the different conditions g and ranges to be measured call for different cir- 15 cuit constants, and the values of the circuit elements of such'instruments vary for almost every installation. This lack of standardization and the consequent necessity of making up special circuit values for each instrument has held up ."-U the production cost. and increased the time requiredlfor manufacture and assembly.

In addition, it has meant that in the eld only the more experienced men could change the ranges of the instruments. Thus, the problem :m of wiring such instruments has acted as a deterrent to their production on an expanded scale.

It is an object of the present invention to provide an improved method and apparatus for completing and housing such circuits in a unim tary mounting, and for making their elements readily changeable in the eld by laymen.

In the present embodiment oi the invention, a standard mounting or housing for the circuit elements of an electrically operated indicator,

5 controller, and/or recorder is provided for housing the circuit elements or parts of such apparatus and the major part of the Wiring necessary to interconnect these elements. This housing unit is also provided with means for detachably Tf" mounting circuit elements such as resistance coils in the housing so that 'the values of the coils may bc changed in the eld by a simple operation without soldering, Welding, etc. This circuit element housing includes all of the wiring neces- 55 sary in such apparatus except those connections to large or variable elements of the instrument. Further, with such a universal circuit element mounting, apparatus such as indicators, controllers, and/or recorders can be almost completely assembled in a manner suitable to .production line assembly without regard to the particular conditions or range of operation of the particular installation for which each instrument is intended. Then the particular elements required for each particular installation may be added by merely inserting previously prepared and predetermined circuit elements in this mounting. In addition, should the conditions or range of operation of a particular instrument need to be changed at a later date; such elements as must necessarily be changed' can be supplied from the factory and inserted in the field by a layman without altering any of the permanent Wiring of the instrument.

This and other apparent advantages are obtained by the method and means described in the following specification and may be more readily understood by reference to the accompanying drawings in which:

Figure 1 is a front elevation of the base of a circuit element mounting unit, with thecover removed, illustrating one embodiment of this invention; l

Figure 2 "is an elevation of the inside of the cover of the mounting shown in Figure 1;

IFigure 3 is a vertical section ofthe base of Figure 1 with the cover of Figure 2 attached,

taken on lines 3-3 of Figures 1; 2 and 4;

Figure 4 is a section taken on line 4--4 of Figures 1, 2 and 3;

Figure 5 shows in perspective one of the circuit resistance elements attached to the base shown in Figure 1; y

Figure 6 is a plan view of the bottom of the base of Figure 1 showing the wiring;

Figure 'Z is a diagrammatic wiring diagram of a typical potentiometer circuit;

Figure 8 shows diagrammatically external connections needed in addition to the connections contained in the circuit element mounting shown in Figure 6 in order to complete the circuit of Figure 7; and

Figure 9 is a table showing the number of resistors of the type shown in Figure 5 necessary to adapt the instrument to certain typical thermocouples and ranges of temperature measurements.

' Referring to Figures 1 and 2, the circuit element mounting shown as an embodiment of the invention herein described, comprises a rectangue lar vertical base plate to which circuit elements such as shown in Figure 5 are attached. A cover 41| housing a standard cell 64 covers the base. Both the cover and base may be made of molded Bakelite or other suitable insulating material.

The circuit elements (Figure 5) or resistor units A, B, C, etc., through J, are attached to the base 40 by a plurality of screws 42 mounted in rows along both sides of the base 40. These screws (Figure 4) are threaded through metal connectors or strips 44 and tightened with respect thereto. The vscrews pass from the back side of the base 40 through to the front and are held by nuts 46. The under side of the base is dished to recess the strips (which act as terminals), and the wiring connections as shown in Figure 6. Each resistor unit has at either end a right angle bracket 48, one side of which is secured to the unit and the other side of which has a hole through which the screws 42 pass. The brackets 48l are clamped between nuts 46 and 52 to provide good electrical connections and to hold the resistor units to base 40.

Referring to Figures 1 and 3, the upper end of the base plate 40 is provided with a plurality of terminals through 8. Each of said terminals comprises a fiat connector strip 54 having terminal screw 5B threaded into the upper end thereof and a second screw 58 threaded through the other end and tightened. Each screw 58 passes through a suitable hole in base 40 and is held in place by a nut 60. Referring to Figure 6 the connectors 44 holding the screws for supporting the resistor units are provided with terminal screws 82.

The base plate 40 is provided at the top with a hexagonal post 31 mounted as shown in Figure 3 by a suitable nut threaded onto a threaded extension of the post extending through the base. The additional nut shown is used to hold a wire connector. Another hexagonal post 34 is secured to the lower end of the base by a thread connection with a screw extending forwardly from the back and locked in place by a suitable nut. 'I'hese posts 34 and 31 act as supports for attaching the cover 4| to the base and also as terminals through which the standard cell 64 is connected into the circuit. A connector plate 86, clamped under post 34, provides an alternate connection, dependent upon the type of thermocouple being used, between one of two terminals 35 and 38 mounted on either side of the post 34. These terminals 35 and 38 are provided with connectors and connection screws under the base similar to those provided on the resistor mounting screws. 42. The base plate 40 is also provided with four holes 68 to receive screws for attaching the mounting to the frame of the instrument.

The cover plate 4|, shaped substantially as shown in the cross sections in Figures 3 and 4, covers all of the resistor units, clamping units, and terminals mounted on the base 40 except terminals I through 8 by which the circuit elements in the mounting are connected to outside elements of the instrument circuit. A cadmiummercury standard potential cell 64, made of glass tubing in the form of an H, is mounted in a recess inside the cover 4| and is clamped in place by two resilient metal strips 1li with its electrode pole vessels 18 extending downwardly. These metal strips 1li run vertically along the inside center of the cover 4| and are each screwed to two brass posts 12 molded into projections 14 extending inwardly in a vertical row along the center of the cover 4|. Cushions of suitable thermal insulation material 16 are placed under the two sides of the cell and around the crossbar of the H at the point where the strips 10 contact it in order to prevent the clamping pressure exerted by these strips from breaking the cell.

The electrodes 18 of cell 64 are respectively connected by a wire 80 suitably soldered to the respective metal mounting strips 'l0 and these strips in turn are electrically connected to posts 34 and 31 on the base 40 by means of screws 82 which pass through holes 84 in the cover plate 4| and clamp the strip 10 rmly to the top of thc posts 34 and 31. The holes 84 are so positioned that cover 4I can be attached to base 40 in one position only in order to eliminate possibility of the standard cell being mounted upside down. This arrangement not only serves to make connections between the standard cell 64 and the wiring connections in the dished portion of the base 40, but also serves to hold the cover 4I in its proper position on top of the base 40 so that it covers all of the circuit elements mounted thereon. It serves to protect them as well as the standard cell 64 from dust, dirt, and other foreign substances, and also serves to maintain all of the circuit elements at approximately the same temperature. At the same time the standard cell 64 is so mounted that it may be replaced easily, if necessary, even by a layman. By having the clamping screws 82 clamped over the metal strips 10 to the metal posts 34 and 31 instead of having them clamp a portion of the Bakelite cover therebetween, any danger of cracking this Bakelite cover by screwing down too tightly on the screws 82 is eliminated, and in addition a good electrical connection is insured between the standard cell and the remainder of the circuit.

Referring to Figure 5, the resistors A, B, C, etc., comprise a spool oi' insulating material having square ends 86 to which the brackets 48 are attached by means of screws 88. The resistance wire which is wound on the spool is of the proper size, resistance, and material, generally manganin, and is soldered at either end to lugs extending from angle brackets 48. The resistance value and other electrical characteristics of each of these resistors is chosen for its relative position in the circuit, the range of temperature to be measured, the type of thermocouple used, and other variables which are dependent upon the characteristics of each particular installation.

Figure 7 shows the wiring diagram of a typical potentiometer circuit such as might be used vin any indicating, controlling, and/or recording instrument responsive to a temperature.

Figures 6 and 8 show the connections necessary under the base plate 40 of the circuit element mounting described herein and the external connections necessary to adopt this mounting unit to an instrument using the circuit of Figure 7. Corresponding elements and terminals of these several figures are identified 4by corresponding numerals and letters. In this circuit a battery S1 supplies current through an adjustable resistor Ra and a current limiting resistor A to the two arms of a potentiometer connected between the terminals 6 and 38, and I8 and 36, respectively. 'I'he rst branch 6 to 38 contains the slidewire resistance R1 and the range changing resistors B, C, and D. In order to permit standardization o1' equipment and quantity production a single design of slidewire R1 of fixed resistance is used, and the potential drop thereacross is selected to suit the particular range of thermocouple being used by selecting the value of the resistors B, C, D, R2, G and F to change the value of current flowing therethrough.

The resistor E is provided to maintain the current drain on the battery S1 approximately constant regardless of the values of the resistors B, C, D, R2, G and F. The second branch of the potentiometer circuit I6 to 36 contains the coldjunction compensation resistance R2 and the re` sistors G and F, the drop across which is compared with the potential of a standard cxll VS2 when calibrating the potentiometer by adjusting resistor R3. These two branches are interconnected in the usual manner by a circuit running from sliding contact 2l) on the slidewire R1 through terminals 2| and 22 of a thermocouple T and through the switches U1 and U2 in their run.positions, i. e., with switch arms 33 and 3| on contacts 23 and 32, respectively, and through the terminals 30 and I5 of galvanometer G to p'oint |2 in the second branch IIS-36. 'I'he standard cell S2 is connected in series with a resistance J and galvanometer G across a portion of the second branch |636 of the potentiometer circuit when the instrument is to be calibrated by moving switch U1 to its check position so switch arm 33 touches contact |4. The resistance J is 'merely a current limiting resistor to prevent the standard cell S2 from being subjected to an overload. The one terminal 34 of the standard cell is connected by a link 66 either to terminal 35 at one end or terminal 36 at the other end of resistance F, depending upon the type of thermocouple employed. Switch U2 is provided to connect resistor H across the terminals of galvanometer G when switch arm 3| is in its zero position (i. e., when it contacts terminal |3) to actas a damping resistor so that the galvanometer zero setting may be adjusted.

Figures 6 and 8 illustrate how the circuit element mounting unit of the present invention is connected to incorporate the circuit of Figure '7. It is apparent .that all of the elements of the circuit are incorporated in this mounting unit with the exception of those which are movable or which must, of necessity, be mounted in some external position. Thus, all of the resistors A through J and the standard cell 64 (Sz), i. e., all of the circuit elements which are fixed in value, are mounted in this housing and are interconnected beneath the base plate 40 by suitable wires 90.

For any given circuit the wiring may be preformed on a template and cabled together as shown in Figure 6. In this manner they may be prepared in large numbers and thus the wiring of the circuit element mounting unit may be done with semi-skilled operators who merely have to place the prepared cable in its proper position and vtighten down the connection screws 62. The only additional connections necessary to complete the wiring of a potentiometer instrument in which this circuit element mounting unit is incorporated, are those connections to those elements of the circuit which include moving parts, such as the slidewire R1, the adjustable resistance R3, the galvanometer G, and the switches U1 and U2, and also those. elements which must necessarily be mounted so that they can be readily interchanged, as well as the coldjuncti'on compensating resistor R2, which must.

be mounted adjacent the thermocouple terminals 2| and 22. These connections to the elements external to the housing may be cabled, and numbered to correspond to the numbers of the terminals to 8.A To further simplify the assembly of the complete instrument these cabled connections may be brought to a common terminal block having numbered terminals corresponding to the terminals on the base 40 and mounted in the instrument in a position adjacent the l place at which the circuit element housing is mounted so that the elements in the housing may be easily connected to the remainder of the circuit by means of jumpers between these adjacent terminals. These latter elements, however, are standard and therefore there is no need to alter their values when changing from one range of measurement or condition to another. Thus, the permanent wiring shown in Figure 8 need not be disturbed when making such changes.

Figure 9 is a table showing the number and position of the resistors which must be inserted in the various positions A through J in the circuit element mounting unit in order to adapt the instrument to various representative types of thermocouples and ranges of measurement. Each 'different value of resistance has been designated by a letter a, b, c, etc., because the actual ohmic values of such resistors might vary widely depending upon the production practices of the particular manufacturer, the types of batteries used, the resistance of the wiring, and other factors which would be constant for any particular type of instrument. These resistors are similar in form to that shown in Figure 5, and they are attached to the circuit element mounting unit by means of the screws 42 and the nuts 52 at the lettered position in the mounting corresponding t0 the letters of the table in Figure 9, for various types of thermocouples, i. e.,

I. C Iron-Constantan Nork Chromel-Alumel Pt-PtRh 13% platinum plus 13% rhodium etc., and for the various temperature ranges listed in this table. The letters in the mounting correspond to the lettered resistances in the circuit of Figure 7. It can readily be seen that a layman with the assistance of a table such as this can, by removing various resistors and replacing them with others of different Value in accordance with the table, change the instrument so that it will operate properly with any type of thermocouple and over any range desired. It is also evident that this change can be made in a short time, with few tools and with little chance of error. In addition, in order to simplify such a change-over, the resistors of different values can be codied by painting them with different colors so that changes for 4various ranges of measurement and to various types of thermocouples may be made in accordance with certain color codes. e

In accordance with the present invention the potentiometer circuit shown in Figure '7 is so designed that a minimum of changes in the values of the circuit elements is necessary to alter the range of measurement and to adapt the instrument to operate with various types of thermocouples. For example, it is apparent from the table shown in Figure 9 that to cover the Wide variety of ranges listed therein with the four types of thermocouples mentioned it is necessary at the most to change only ve of the fixed resistor units mounted on base 40, and frequently only three or four need to be changed.

As many embodiments vmay be made of the above invention and as many changes may be made in the embodiment above described, it is to be understood that all matter hereinbefore set forth or shown in the accompanying drawings is to be interpreted as illustrative only and not in a limiting sense.

We claim:

l. As an article of manufacture, a universal circuit unit for electrical measuring apparatus, comprising, in combination, a base of insulating material, a plurality of terminals mounted in a row across one end thereof, a plurality of circuit elements detachably mounted in a row on said base, connections between said circuit elements and said terminals, said base being adapted to support said connections on the side opposite said circuit elements, a cover for said base covering all of said base but that portion on which said terminals are mounted and forming therewith a housing for said circuit elements, another circuit element mounted on the inside of said cover, and means for attaching said cover to said base and for serving as connections between said latter circuit element and certain of said rst mentioned circuit elements and terminals.

2. As an article of manufacture, a universal circuit unit for electrical measuring apparatus, comprising, in combination, a rectangular base of insulating material, a plurality of terminals mounted in a row across one end thereof, a plurality of yconnectors mounted in two rows, one row along each side of said base perpendicular to said row of terminals, a plurality of circuit elements mounted between opposite connectors in said two rows, connections between said connectors and said terminals, the underside of said base opposite said circuit elements being dished `to receive said connections, a cover for said base covering all of said base but that portion on which said terminals are mounted and forming therewith a housing for said circuit elements, another circuit element having two terminals recessed in. the inside of said cover, two separated metal strips secured to said cover for yclamping said latter circuit element in said recess, each of the terminals of said latter circuit element being connected to one of said strips, two metal posts mounted on said base, connections between said posts and certain of said connectors and terminals, and a screw passing through each of said strips and threaded into one of said posts for attaching said cover to said base, whereby said strips and posts serve to secure said cover to said base and act as connections between said latter circuit element and the remainder of the circuit of said electrical measuring apparatus.

3. For use in connection with an electrically operated measuring instrument having an electrical circuit containing interconnected fixed, variable, and movable circuit elements for measuring the value of a condition, a housing unit for said xed circuit elements of said instrument, said housing unit being removable from said instrument as a unit, and comprising, in combination, a base on one side of which are mounted said xed circuit elements, a plurality of terminals mounted along one end of said base, connections on the other side of said base for electrically interconnecting certain of said elements and for connecting certain of said elements with said terminals, each of said elements being provided with attachment means at either end for securing it to said base, means for making suitable electrical connection between said lastnamed means and the connections on the other side of said base, and said attachment means being readily detachable whereby said elements may be changed or interchanged.

4. For use in connection with an electrically operated measuring instrument having an electrical circuit containing interconnected xed, variable, and movable circuit elements for measuring the value of a condition, a housing unit for said xed circuit elements of said instrument,

' said housing unit being removable from. said instrument as a unit, and comprising, in combination, a base on one side of which are mounted said fixed circuit elements, a plurality of terminals mounted on said base, connections on the other side of said base for electrically interconnecting certain of said circuit elements and for connecting certain of said elements with said terminals, each of said elements being provided with attachment means at either end for securing it to said base, means for making suitable electrical connection between said last-named means and the connections on the other side of said base, said attachment means being readily detachable whereby said elements may be changed o-r interchanged, a cover for said base forming therewith a compartment, said cover supporting on its inner side certain other of said circuit elements, and means for securing said cove-r to said base and providing an electrical connection between said other circuit elements and the connections on the other side of said base.

5. For use in connection with an electrically operated measuring instrument having an electrical circuit containing interconnected xed, variable, and movable circuit elements for measuring the value of a condition, a housing unit for said xed circuit elements of said instrument, said housing unit being removable from said instrument as a unit, and comprising, in combination, a base on one side of which are mounted said xed circuit elements. a plurality of terminals mounted along one end of said base, connections on the other side of said base for electrically interconnecting certain of said elements and for connecting certain of said elements with said terminals, each of said elements being provided with attachment means at either end for securing it to said base, means for making suitable electrical connection between said last-named means and the connections on the other side of said base, said attachment means being readily detachable whereby said elements may be changed or interchang'ed, and the terminals on said end of said housing matching terminals in said measuring instrument when said housing is secured in place.

6. For use in connection with an electrically operated measuring instrument having an elec.. trical circuit containing interconnected xed, variable. and movable circuit elements for measuring the value of a condition, a housing unit for said xed circuit elements of said instrument, said housing unit being removable from said instrument as a unit, and comprising, in combina- 'tion, a base on one side of which are mounted said fixed circuit elements, a plurality of terminals mounted on said base, connections on the other side of said base for electrically interconnecting certain of said circuit elements and for connecting certain of said elements with said terminals, each of said elements being provided with attachment means at either end for securing it to said base, means for making suitable electrical connection between said last-named means and the connections on the other side of said base, said attachment means being readily detachable whereby said elements may be changed or interchanged, a cover for said base forming therewith a compartment, said cover supporting on its inner side a circuit element adapted to operate only when right side up, means for securing said cover to said base and providing an electrical connection between said latter circuit element and the connections on the other side of said base, said means being so designed as to permit the cover to be attached to the base in only one position whereby the latter circuit. element is always mounted in an operative position when said base is properly attached to said instrument.

7. For use in electrical measuring apparatus having a circuit including a plurality of circuit elements, a combined circuit element and 'connection housing unit, comprising, in combina.-

20 tion, a base, a series of pairs of spaced connecting brackets mounted on one side of said base, a plurality of connectors, each bracket being secured Ato the base and electrically connected through its securing means/to said connectors on the other side of said base, each pair of brackets being adapted to receive oner of said circuit elements', a cover for said brackets and said circuit elements being dished to receive another of said circuit elements, means to secure said latter circuit element in said dished portion of said cover, means for securing said cover to said base and for connecting the terminals of said latter circuit element with the connectors on the other side of said base, a series of said binding posts on the front side of said base, and 

